Cellular communication networks evolve towards higher data rates, together with improved capacity and coverage. In the 3rd Generation Partnership Project (3GPP) standardization body, several technologies have been and are also currently being developed.
LTE (Long Term Evolution) is a recent standardised technology. It uses an access technology based on OFDM (Orthogonal Frequency Division Multiplexing) for the downlink and Single Carrier FDMA (SC-FDMA) for the uplink. The resource allocation to wireless devices (also known as user equipment, UEs) on both downlink and uplink is generally performed adaptively using fast scheduling, taking into account the instantaneous traffic pattern and radio propagation characteristics of each wireless device. Assigning resources in both downlink and uplink is performed in the scheduler situated in the radio base station.
However, for periodic low volume traffic, such as for voice (e.g. using VoLTE, Voice over LTE) and other QoS (Quality of Service) applications, such dynamic scheduling consumes a significant amount of overhead in comparison to the payload traffic. In order to reduce this problem, semi-persistent scheduling (SPS) has been introduced to reduce the signaling overhead for periodic traffic.
On the one hand, SPS takes care of stable periodic transmissions efficiently. On the other hand, SPS does not efficiently handle variations in the periodicity very well, often causing a fall back to the dynamic scheduling with a relatively high overhead.